In general, there's a good reason for heating the water overnight: electricity is often cheaper at night, and (on a national level) it means that electricity demand is spread more evenly over the whole 24 hours.
This is a good idea, but are you by chance located outside the US? Every water heater I've personally encountered in North America has been powered by natural gas. Even so, it only takes an hour or so to fully replenish the hot water, so it still makes sense to allow the water to cool down between, say, midnight and 5am.
Huge swaths of the U.S. simply don't have natural gas. The township that I used to live in explicitly stated in their planning that they did not intend to run gas lines.
Electricity is cheaper at night (from some utilities) because the demand is a lot lower at night. But why is it a good idea to heat water at night when I'm not going to use it?
And as others have pointed out I have a natural gas heater.